Balanceable network electric measuring system



Sept. 30, 1952 A. J. HoRNFl-:CK 2,512,528

E BALANCEABLE NETWORK ELECTRIC MEASURING SYSTEM Filed Aug. 2, 1947 2sHEETs-SHEET 1 Sept. 30, 1952 A. J. HoRNFEcK 2,612,628

BLNCEABLE NETWORK ELECTRIC MEASURING SYSTEM Filed Aug. 2, 1947 2SHEETS-SHEET 2 ANTHONY J.HORNFECK BY 2% ffm/w24 .A RNEY Patented Sept.30,.1952

EALNCEABLE NETWORK ELECTRIC MEASURING SYSTEM Anthony-3:'. 'HornieelnVLyndhurst, Ohio, assignor to Bailey Meter Company, a corporation ofDelaware Application August 2, 1947, Serial No. '765,760

5 Claims. (Ci. 318-28.)

My invention relates toA electric .measuring systems which areresponsive to one: or more variable conditions and operate to measurethe variable or some function of the variables.

The measurement of a variable condition is frequently accomplished byeiecting yan unbalance of a balanceable 'network in accordance withvariationsin the condition and causing means to operateas -a result ofsuch unbalance and return the network to a balanced condition. It isnecessary withsuch a system to provide leads from the balanced networkhaving resistances so designed' as' to subject the operating means onlyto voltages proportional to thel actual unbalance of. the; network. Whenthe changes offtheyariable condition' .arefpsuch as to eiect /only'avery slight unbalanceoi the-network.; it is 'difficult to" produce achange in `-a resistance of the -network to; returnv the latter to abalanced condition. .Instead of rebalan'cing the; networkwit .has vbeenIfound that better results may be obtained by subjecting the outputvoltageof. the network to' an opposing.. voltage-which. is regulated by'mea-ns operating in response-ite the difference ybetween the twovoltages.Ik .Af-close adjustmentof the opposing volt.- age maybef-obtained becausensubstantial.operar tion of theopera-ting meansfcanbel made to produce: only slight changes in voltage. rllhe re;-sistancesof the leads from the .networkfwithsuch anA .arrangement do`not vaiiect thev operationy of the system. This Yarrangement does.require, howeventhat the voltage applied to thev network for energizingthe latter.,` `antivol-tage applied tothe `-system` for producing` theopposing. voltalge, bemaintained vdirectly proportional to each other.`'If'the system i's .to operate on. directeurren't, separate sourcesoff'power must .be providedffor the network and the opposing` voltage,and regulators are 'then required to maintain the desired' voltagerelationship. B'y operating, the ,Systemy on alternating current, theinput voltage forthenetworkand the opposingvoltage maybe" obtained 'fromthe samesource 'ifa trans.-

f former is usedin transmitting` power to atleast one yportion of" thesystem.. so that 'the separately energized partsV are insulated .fromeach other.. Anyv changesin the voltage at theV sourcefwill thenbe'reflected propnr'ti'on'at'ely tov both ends of the' network.'Ifdesiredthe input voltage to thefnetwork may be varied in accordance.with one 'variable while the network balance' is varied intaccordancewith one or morevarables. Regulation of the voltage opposing the .outputof the network is then an indicationsotsomefunction-of- `the variables.By varying the output of one net.- Work in response to changes inonetor'morexvari ables and yopposing this output .by a voltage whichiscaused to vary inresponseto other 'varia ables, as wellV as by meansoperating on .a dif.- ference between the voltages. indications :may beobtained of other functions. of the variables.

An object of my .invention is to provide'improved systems .for measuringvariables. Another object is to providewan .improved -measuring systemin which ther voltage output;v oi a networkresponslve to one; ormoreVvariables: is opposed by a voltage regulated `by means operating invresponse to differences betweenthev voltages. YetA another vobject isto provide annimproved measuring system having means for' producingopposing voltages varying vin response 'to variables and broughtv intobalance with each other by means operating in response to .diiferencesbetween the voltages. Other objects will appear in the course oftheifollowin'g` description.

In the accompanying drawings there are shown for purposes ofillustration several forms' which my invention' may assume in practice.

In these'drawings:

Fig. l is ay schematic diagram of a. `system including a bridge circuitwhich is unbalanced in response to a variable and has its output voltageopposed by another voltage.y regulated. by means operating in responseto thel differences between the voltages.

Fig. 2 is similar to Fig. l but has means'tor varying the input to thebridge in response to ;a variable while the bridge unbalance isdetermined by two variables.

Fig. 3 shows two bridge circuits unbalancedin response to variables andoperating together to determine a `voltage which is to be measured;

Figs. 4 and 5 show systems in which voltages produced as a result of theunbalance of sepa.- rate bridge circuits are vopposed to each other indetermining the voperation of means for regulating one of the voltages.

Fig. 6 shows a system in which the output voltage of a bridge unbalancedby a variable-condition is opposed bythe output voltage of anotherbridge which is adjustable to balance the sys- Referring to the drawingsit will be noted that there is shown in Fig. 1 a system whichis adaptedto measure changes in a single variabler-condi-` tion. This systemincludes a Wheatstone bridge I .having an. element 2 formingk one of4its legs and Varying in resistance inY response to` changes in thecondition, a xedresistance 3lforming a second leg, and fixed resistances4 and 5 combined with portions of the potentiometer 6 to form the thirdand fourth legs. A contact 1 is adjustable manually to divide thepotentiometer resistance between the third and fourth legs so that thepoint from which changes are to be measured may be varied at will. Thecontact 1 is connected by a conductor 8 to one end of the primarywinding of a transformer 9, and the other end of the primary winding isconnected to a contact I of a potentiometer Ii. One end of thepotentiometer II is connected by a conductor I2 to a point on the bridgebetween the resistances 2 and 3. A transformer I4 has a primary windingI5 connected to a source of alternating current, and a pair of secondarywindings I6, I1, the Winding I6 being connected to diagonally oppositepoints of the bridge for energizing the latter, and the winding I1 beingconnected with an adjustable resistance I8 across the potentiometer II.The secondary winding of the transformer 9 is connected to an amplifierand motor control device which effects operation of a motor 2| in onedirection or the other depending upon the phase of the voltageenergizing the transformer.

The connection of the secondary winding I1 to the potentiometer I I issuch that the Voltage drop in the potentiometer opposes the voltageoutput of the bridge in determining the flow of current through theprimary winding of the transformer 9. When the bridge output exceeds thevoltage drop in the portion of the potentiometer between the contact I Dand the conductor I2, the current flow through the primary winding ofthe transformer 9 is such as to effect opera- -tion of the motor 2I in adirection to position the contact I0 through a connection 22 so as toincrease the portion of the potentiometer connected in the outputcircuit of the bridge. If the condition changes so that the bridgeoutput drops below the opposing voltage from the potentiometer, themotor operates in a direction to reduce the portion of the potentiometerconnected in the bridge output circuit. An indicator 23 is operativelyconnected `to the motor for indicating on a scale 24 the value of thecondition.

In Fig. 2 there is shown a bridge 26 similar to ythat-of Fig. l buthaving resistances 21, 28 `forming diiferent bridge legs and varying' inresistance in response to changes in temperature at different points ina conduit 29 conducting uid, such as steam. For energizing the bridgethere is provided a transformer having a primary winding 3D connected toa source of alternating current, and a pair of bucking secondarywindings 3|, 32 connected to diagonally opposite points of the bridge. Acore member 34 is supported by a float 35 for movement between theprimary and secondary windings, and pressures at opposite sides of anorifice 36 in the conduit 29 are supplied through conduits 31, 38 toopposite surfaces of the float for determining the position of thelatter in a sealing liquid within a container 39. The oat shown hereinis so shaped that the position of thecore member 34 is changed inresponse to changes in the rate of fluid flow. The output conductors 8and I2 of the bridge are shown in this case connected with the Variableportion of the potentiometer I I directly to the input terminals of theamplifier and motor control device. The potentiometer II is energized byits direct connection to the source of alternating current throughconductors 40 and 4I.

- When the core member 34 is centered with respect to the secondarywindings 3 I, 32, the voltage input to the bridge is zero, and thisposition of the core member is obtained when there is no flow of fluidin the conduit 23. As the core member is moved from its centeredposition, the voltage induced in one of the secondary windings isincreased while it is decreased in the other winding, and the changes inthe induced voltages are in direct proportion to the distance that thecore member moves. The voltage E1 across the secondary terminals andapplied to the input terminals of the bridge is then directlyproportional to the rate of fluid ow. Representing the flow of the fiuidby the letter Q, the following equation holds:

Where Kira constant.

The unbalance of the bridge is equal to the difference between theresistances 21, 28,' and the values of these resistances are directlyproportional to the temperatures at the points Where the resistances arelocated. The voltage output of the bridge is proportional to the voltageinput times the bridge unbalance. If the temperatures at the resistances21, 28, are represented by T1 and T2, then the Voltage output E2 of thebridge is indicated by the following equation:

where Ko=a constant.

In Fig. 3 there is shown a system in which a voltage determined by theunbalance of two bridge circuits is opposed by the voltage drop across aportion of the potentiometer I I. In this case, bridge circuits 45, 46are each provided with fixed resistances in three 'of its legs and aresistance forming the fourth leg varying in value in response tochanges in somecondition. The values of the variable resistances inbridges 45, 46 are each representative of a condition and have beenindicated by X and Xi respectively. lThe secondary windings 48, 43 of atransformerare connected to diagonally opposite points` of the bridgecircuits for energizing the latter, and a third secondary winding 50 isconnected with an adjustable resistance 5I across the potentiometer I I.A primary winding 52 is common tothe three secondary windings and isconnected to a source of alternating current. Connected across thevbridge circuits at points between the connections to the secondarywindings are potentiometers 54, 55 having adjustable contacts 56, 51.The contact 56 is shown connected to one end of the potentiorneterresistance 55 while the contact 51 is connected to one end of thepotentiometer resistance II. One end of the potentiometer 54 and thecontact IIJ are connected to the amplifier 20 by conductors 59 and 6U,respectively. `Unbalances of the bridge circuits 45, 46 result involtage drops` across the potentiometers 54, 55, and the output voltagesof thebridges are dependent upon the unbalance as well as the positionsof the. con-J tacts 56, 51. These contacts are adjusted manu'- ally topredetermined positions and then Aleft in such positions. bridgesrepresented by E and E1 vary directly in proportion to the changes inthe condition, ,as shown by the equations:

I E=IfXA E1=,K1Xi Where K and K1 areconstants,

The voltage outputs of. 'the'lWith:tliezbridgesconnectedtintotlrewsystem as showin theavoltages-outputsadd to? opposeithe voltage -Eaff across, anr:adjustable' portion oir ythe. potentiometer" II. Any; voltage-.idifference#` bee tweenl the; voltage.` Ez and? thesumi of; E; and: E1;causes the motorzII tof-operate:andpositionxhe; contact` I0 through@`thef connection? 22- until E2. equals the total ofLEand Ei..The.'positionizoflthe contact f I 0, is?w then. representative r off thetotal. of the conditions and: Xi; sincev Ez'. when:` the sysz-f tern-isbalancedisfequal I tosKii'X-sxni where'sKz'- isi-ar'onstant.lByreversing:theconnectlonsifrom' the/:r conta-ctx 56` andi thel-endfoffr thezpotentiometer 54, Ez will be representative oftheidiierencebetween Xand'Xi:v

'Elige shower-a:- systenr-inwhichtwo bridgewcircuit'sf` 04;fhavegtiieirf output' voltages opposed tofeachfotlierltr-determining:tnefoperatien of theVZ motor 22I. Ea'cn-oifthe1bridgesihas-#one lleg vary-e ingfin resistanceinlresponseto'fchanges2inavarih able, the resistances or variablesbeing; indica-ted? by X- and" Xi; Tliednput' to bridge 6"# is deter#vmined byl the positioning'foff a; contact 66'l on av potentiometer' 61by: a1 device; suclil` as al Bourdon' tube 68, responsive tosme^variab1e condition;l

such asl tempera-ture or" pressure: The inputjt'obridgejil is variediina similarmannerbya` Bour= don tuben 69 operating in responsetoa:-variable for positioningfa contact'10'alorrge; potentiometer 'I I. Thelpotentiometersky 6T and" 11i 'are ener--` gi'zed' by= secondary'windings 12; 'leef` a train'- former' navingits= primary winding 'Ilconnected to asource of power. Tl'ieilvcltage outputs-:ofthe bridges64;,65 are;appliedtopotentiometers `v15;,16 which are connected at oneendflby a conductor 'I1`and havetheir adjustable contactsTBQTS con?"Vnected to the ampliier 20 controlling theoperaf tionrof themotor 2|.Operative, connections l2 between the motorfandlthe. contact 18`determine the position ofthelatter.. Y

The voltages. appliedltoy the. bridges-464', Ii5'vareVA representativeofthe posi ionsoficontacts 66,110 which in turn are representative ofthe variables acting onthedevices 68; 60: These variables may bedeslgnatedrby the. letters Sv and S1, respectively. The voltage output"ofthe bridge 64 is then equal to l KSX while' the: outputr ci"v bridge65 is KiSiXi. The Voltage dropin the portion off' the potentiometer:1G-'between the:` contact 'I9 and the conductor I1 opposesthe voltagedropin the portion of the potentiometer between-the contact'l andtheconductor 11.' The difference between these voltages causestliemotorto.operatelandtposition the contact' 'Iiiuntil the 4,voltages are equal.The 'position ofthe contact 18'. i's-.representative off. a lmeasuredvalue, which'` maybe indicated .by the letter Y; and tlefcontactfli)Jmay be positioned manually toobtain fromv thefpotentiometerV "I6 a fixedor a varablevoltageiwhch may bev indicated by therletter' Yi. Whenthevoltage input to the amplifier iszzero, tliexfollowingfequationszapplyz,

Reggiseno g Kf SXJ Assuming K1=K then c SlXiYi IY SX Fig. shows a systemsimilar to that of Fig. 4 with the unbalance of the bridge 64 determinedbis? a resistance 82frwhicht iszvariedazbyf ae devicessucliaa'sfaBourdorrvtube83;operatingirrzresponsei to: changes: in; atcondition. such; as: pressure in azconduiti; andi the unbalance-:of thebridgefdeterminediby arresistance'BS varyingin'response:tow/temperature: at: some point@r in: the conduit: The inputito therbridge. 04,1 isf determined: bythe: positioningfof Va .core memberil.Yrelative toibuck'-v ing-csecondaryf'windingsl 81,. 881: of'A ai:transformer; irnresponse to; diierentials:impressure at; oppozfvsitersi'desi-of: aniori'ce 891 arranged-in tlfrexconduil.-4 The voltageoutput iofa; tliesbridge` 64'1 is 'opposed to;` thatzofr-bridge-I'to'd'etermine `the;vvoltageaps4 plied; tottlieiV amplifier: 2 0.; iand,themotorsfzli posie tionsathe' corez member k90z-frelativre to;bucking? secondary Windings:19.fI:,-. 92, to?` determineftle volteYage-input; to bridget 65. The; output voltagesoilr eaclii. bridge: isproportional; tor itsy input: voltage tirrresfitsiunbalance.-yThe;input-voltageitmbridgea 64 is proportional to thepressuredi'fferentialsi aorosslthe oriice 89. and1 maybe representedbythe letten The: input voltage.- to'f bridgeti 'is representative: of.the positions of'. the corel member` ;-and1.this'value may" berepresented: by' the =v letter." Z; The' unbalances: ofi bridges. 64,:652` are; proportional. to the: pressure P and; chez temperature T,respectively; the conduitz'BLl The output voltages: of the' bridgessxk,65.' may: then'sbe represented by theequationsz: E1k==K1`HP Efzv-Kz'ZT vWhen: the output i voltagesrare-equal'x andi thea. system,isf,balancedVthen and' is shown by the indicator 23; Y

Bridge circuits' are frequently provided with resistancesformingdifierent legs and varyingin valuewithrespect to each other onchanges in ay condition to be measured In Fig. 6i Illfiave. shown abridge including resistance elements;A Xy in two of' its' legs'andrresistance elements Xi, in tli'e'otlrer two legs. The elements X areadapte ed tov change in resistancev equal. amounts; in onev directionwhile` the elements X1 change equal amounts in the opposite directionwith changea; ina condition to be` measured. A bridge similar. to thisis` used in some of the gages. available. for measuring vstrain'. Thisbridge does; not inclu'de means which is, adjustable for vary.ing'the1-point from' which theV measurements; of the condi'- tion may beobtained. In order'thatthe pointf from which measurements aremade` maybe; adjusted' and that, measurements vof the values; from such point maybe obtained. therev are pro#` vided conductors, 91 from'the outputterminals of'the bridge to movabley contacts 9&99 of' poetentiometerslll, I0"I connectedat their ends. and energized from thesecondary windingv |03 of'r af transformer IM.. An amplifier and motoriconf trol device 20 is connected in circuit with the" conductor 96 andcontrols the operation ofthe motor 2I which positions the contact 98through connections 22. The contact 99 is adapted to be positionedmanually. A secondary winding |05 of the transformer |04 is connected tothe bridge 95 for energizing the latter. It will be seen that thepotentiometers |00, IOI with their adjustable contacts98, 99 formabridgecircuit'and the -output voltageioi this circuit opposes' theoutput 'voltage' of thebridge 95 to determine vthe iiow of currentthrough theampliier and .motor control device '20. .An unbalancefof theoutput voltages resultsin an operation of the motor 2| to positiontheicontact 98 untilthe opposing voltages are equal. An adjustment ofthe contact 99 results in a change in the positions ofcontact 98toproduce a balance y.for predetermined conditions to befmeasured. The'positions of contact are representative of the conditions measured, anda changing of .these positions by adjustment Voi.' contact 99 merelyresults in an indication of the values from a different zero point.l Itwill be noted thatxthis arrangementmakes it possible to readfthe valuesas they change in either direction from theV zerorpoint since thevoltage output of the two `bridge circuits are always in opposition toeach other.

As aresult of my invention there are provided improved systemsk formeasuring a variable or some function of a plurality of variables. vIneach system there is provided one or more bale anceable networks .whichare unbalanced onvvari- 'ations 'of a condition and produce'a voltage tobe. measured. The measurement of the voltage is accomplished ini eachcase by regulating an opposing voltage until itris' equal to Ythevoltage to be measured. Although some of the systems have been shown anddescribed as indicating functions of certain'variables, it will beunderstood that they'may be applied as .well to the indication offunctions of other variables.

While there are shown in this application several forms which myinvention may assume in practice, it will be understood that' theseforms of the same are shown for purposes oi' illustration and myinvention may be modified and embodied in various other forms, withoutdeparting from its spirit or the scope of 'the appended claims.

An application, Serial No. 280,307, iiled April 3, 1952, is a divisionof this present application.

WhatI claim asY new and desire to secure by Letters Patent of the UnitedStates is:

1. A measuring system for a plurality of interrelated variableconditions comprising, in comb*- nation, a pair of bridge circuits eachhaving an element forming one of its legs and varying in resistanceinresponse to changes in a, diiferentone oi" said conditions, means forenergizing said bridge circuits from a common source of voltage, meansfor varying said voltage for each bridge in response to changes indifferent other ones of said conditions, means for opposing a voltageproportional to the output voltager of one of said bridge circuits to anadjustable portion oi the output voltageof other of said bridgecircuits, and means operating in response to the difference be#tweensaid voltages for. varying the portion of the output voltage ofsaid other bridge circuit until'said opposing voltages are equal.

2."A measuring system for a plurality of interrelated variableconditions comprising, in combi-v nation, aV pair'ofib'ridge circuitseach having an element formingone ofV its legs and varying` inresistance'inresponseto changes in a different one of. said "conditions,/meansfrlforL energizing said bridge circuits from a commonso'urcero'fvoltage, meansl forvarying said voltage for; one of the bridgesine'sponsestolchanges-in a differentone of. said. variable conditions,apotentiometerconne'cted across the output connections of one of saidbridgev circuits, means Vfor. opposing a voltage proportionalto theoutput voltage of the other Vsaid bridge circuitsto a `variable portionofthe voltage drop 4across: said potentiometer, and.. vmeans responsive4to the diierence` between said opposing voltages, for varying the:portion of the,voltage drop across said potentiometer until saidopposing voltages are equal. 1: ,v :u fi i.

3. A measuring system for a pluralitytn'.l interrelated variableconditions :andadapted tocombine. the individual: measurementscornprisilns in combination a Wheatstone bridge including Aresistors,atleast one of said resistors being varied in resistance inV responsegtoar change- 4'in one vof saidvariable conditions, means of energizingsaidbridge from aj isolurcepfalternating current. means tog-Giust thevoltage of saidA alternating currentin-response to a change in anotheroisaid variable conditions, means including a potentionreter energizedfrom saidsource,adjustable means for opposing a variable portiondf'the'voltag'e drop across 'said potentiometer to th'e'output voltage ofsaid bridge and mean's. operating inresponse to the vdifferencebetweer'ijtlifeV variableportion of said potentiometer voltage and saidbridge' output voltagefor adiustingsaid adjustable meanstoredu'cesaid'differencetozerjol"v i 4. vThe,measuringjsysternas den'edinclaim 3 in Whic'ilrij- `the means to' adjustthe'voltage of thealternating lcurrent energizing the bridge is ar- 1"anged1 to'ma'intainthe same jphase kof output thrdushgiit itsgranse ,1 i"5:'The`measuringisystem as defined in claim 4 in which' two of-thebridgeresistors are xedin value and the remainderj'ae variedin'resistance each in-response to aichange in? a diiferentjone ofsaiclvariable conditionsA I` l,

" 'ssrsonsnsoamca j 'QREFRENCES'CITD ,"YIhe following referencesflare of'record in the ille ofgthis patent:vv 4, y,

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